The gateway drug theory (also called gateway theory, gateway hypothesis and gateway effect) is the hypothesis that the habitual use of less deleterious drugs may lead to a a future risk of using more dangerous hard drugs and crime.[1]

Some research suggests that some serious drug abusers have used other drugs before using marijuana or alcohol.[5]
Individual drug-abuse histories show that "hard drug" users do progress from one drug to another, but the research is not clear enough to confirm the gateway theory.[6]

Some recreational drugs have many pharmacological similarities, which the theory claim is the reason for the escalation.

Contents

A stratified, random sample of 1943 adolescents was recruited from secondary schools across Victoria, Australia at age 14–15 years. This cohort was interviewed on eight occasions until the age of 24–25 years. At age 24 years, 12% of the sample had used amphetamines in the past year, with 1%–2% using at least weekly. Young adult amphetamine use was predicted strongly by adolescent drug use and was associated robustly with other drug use and dependence in young adulthood. Associations were stronger for more frequent users. Among young adults who had not been using amphetamines at age 20 years, the strongest predictor of use at age 24 years was the use of other drugs, particularly cannabis, at 20 years.[7] Those who were smoking cannabis at the age of 15 were as much as 15 times more likely to be using amphetamines in their early 20s.[8]

Multiple scientific studies show that the consumption of cannabis can possibly predict a significant higher risk for the subsequent use of other "harder" illicit drugs, while other studies show that it cannot.[9][10] Two recent studies are from University of Pittsburgh's School of Pharmacy,[11] and from Dr. Michael Lynskey.[12]

In 1999, a study by the Division of Neuroscience and Behavioral Health at the Institute of Medicine entitled "Marijuana and Medicine: Assessing the Science Base," found no evidence of a link between cannabis use and the subsequent abuse of other illicit drugs on the basis of its particular physiological effect.[13]

In December 2002, a study by RAND regarding if cannabis use results in the subsequent use of cocaine and heroin was published in the British Journal of Addiction, a peer-reviewed scientific publication. The researchers created a mathematical model simulating adolescent drug use. National rates of cannabis and hard drug use in the model matched survey data collected from representative samples of youths from across the United States; the model produced patterns of drug use and abuse. Andrew Morral, associate director of RAND's Public Safety and Justice unit and lead author of the study stated:[14]

We've shown that the marijuana gateway effect is not the best explanation for the link between marijuana use and the use of harder drugs ... An alternative, simpler and more compelling explanation accounts for the pattern of drug use you see in this country, without resort to any gateway effects. While the gateway theory has enjoyed popular acceptance, scientists have always had their doubts. Our study shows that these doubts are justified.

In 2006, the Karolinska Institute in Sweden used twelve rats to examine how adolescent use of cannabis effects subsequent abuse of other illicit drugs. The study gave six of the twelve "teenage" (28–49 days old, or 6.6–10.4 in human years) rats a small dose of THC, reportedly equivalent to one cannabis joint smoked by a human, every three days. The rats were allowed to administer heroin by pushing a lever and the study found the rats given THC took larger doses of heroin.

The current findings support the gateway hypothesis demonstrating that adolescence cannabis exposure has an enduring impact on hedonic processing resulting in enhanced opiate intake, possibly as a consequence of alterations in limbic opioid neuronal populations.[15]

The institute examined the brain cells in the rats and found THC alters the opioid system that is associated with positive emotions, which lessens the effects of opiates on rat's brain and thus causes them to use more heroin.[16] Paul Armentano, policy analyst for NORML, claimed because the rats were given THC at the young age of 28 days, is impossible to extrapolate the results of this study to humans. Also, cannabis exposed adult rats, despite being desensitized to heroin, were in another study, no more likely to get addicted than the controls.[17]

In December 2006, a 12 year gateway drug hypothesis study on 214 boys from ages 10–12 by the American Psychiatric Association was published in the American Journal of Psychiatry. The study concluded adolescents who used cannabis prior to using other drugs, including alcohol and tobacco, were no more likely to develop a substance abuse disorder than subjects in the study who did not use cannabis prior to using other drugs.[18][19]

One reason the risk factor for abusing drugs in cannabis users is higher because few people try hard drugs prior to trying cannabis, not because cannabis users increasingly try hard drugs such as amphetamines.[20]

According to the NIDA, "People who abuse drugs are also likely to be cigarette smokers. More than two-thirds of drug abusers are regular tobacco smokers, a rate more than double that of the rest of the population."[21]